1. Technical Field
This invention relates to a pressure measuring system, a pressure measuring sensor assembly, a vessel adapter, a ventilator system, a blood pressure measuring system and a method for measuring pressure.
2. Background
Flow and pressure of air in the lungs are important data for intensive care ventilators and anesthesia machines. In fact, monitoring of these parameters is mandated by the pertinent standards today. There is consent among the experts that measurement directly at the airway opening is the best way to measure. However, water vapor condensation, mucus, blood, and possibly other body fluids as well as infectious agents may be present in the airway tubing and present a serious threat to reliable and accurate measurement and patient safety. For this reason, most intensive care ventilators and anesthesia machines measure within the machine and not at the airway opening of patients. On-airway sensing is available only on a few intensive care ventilators. These devices connect the airways to the internal sensors by means of sensing tubes and thus allow “remote” sensing of airway pressure and differential pressure, for example across a flow-measuring restrictor, as disclosed in for example U.S. Pat. No. 4,083,245. The reasons for using sensing tubes are two-fold: first, the pressure sensors need periodic baseline resets and the necessary valves are too heavy to be put at the airways; therefore they are located within the ventilator or anesthesia machine. Second, the relatively long tubes provide a certain separation between airways and the device, thereby protecting the pressure sensors within device from moisture and contamination with bacteria and viruses. However, protection from contamination is not complete and water vapour can easily move into the sensing tubes by means of diffusion. For this reason, a continuous or sporadic purge of the sensing tubes is necessary.
While the state-of-the-art is working well, it has a number of disadvantages: the sensing tubes are prone to kinking and disconnection, the purge flows interrupt the measurement process and introduce measurement errors and thus need to be checked regularly, disconnection of sensing tubes is difficult to monitor by the ventilator or the anesthesia machine and is a safety concern, and contamination of the sensors is not completely avoided if the purge flows stop—for example if the ventilator or the anesthesia machine is stored with the tubing still attached. Finally, the response time of the ventilator or the anesthesia machine is degraded by long sensing tubes and this limits the rapid response to breathing efforts of the patient, for example in Automatic Tube Compensation. Such limitation may be so strong that spontaneous breathing becomes impossible if the patient is very weak, and this in turn will lead to longer time on the ventilator with associated risks for infection, complications and death. US patent application US 2007/0261498 A1 discloses a respiratory pressure sensing system which consists of an airway adapter (“pneumotach”) and a pressure transducer. The transducer is designed to receive a respiratory sample when it is coupled with the airway adapter. This system is configured to be coupled directly, without long tubes between said two system components. Pressure ports of the transducer are in gas flow communication with the airway adapter conduit. And consequently during pressure measurement the differential pressure sensor is in direct contact with the respiratory air in the airway conduit. It is suggested to use filters such as hydrophobic, antimicrobial filter materials, e.g. in the form of felt or particles, to prevent microorganisms, moisture, and other contaminants from passing through the coupling ports into conduits of the reusable transducer. However, the filters proposed in said document are gas permeable, in fact they shall not substantially restrict the flow of sampled respiratory gases through pressure ports. Thus contaminated patient air still may reach transducer parts and therefore diminish its reusability. Further protection of pressure or flow transducers is, thus, desirable. For the reasons described above, there is a clear need for a sensor system providing higher patient safety and higher measurement reliability. At the same time costs of such a system should be low.